The present invention concerns in general a high-voltage regulator circuit enabling at least a first regulated output voltage to be delivered from a high input voltage, in particular of the order of several tens of volts. More particularly, the present invention concerns a high-voltage regulator of this type in the form of an integrated circuit controlling an external regulating device.
Various applications require the supply of a determined regulated voltage from a high input voltage, this regulated voltage being used in particular for powering the electronic circuits of an associated device. FIG. 1 shows a regulator circuit globally designated by the reference numeral 1 including an external regulating device 2, formed of a JFET transistor, and a control circuit 10 for this external regulating device 2. This regulating circuit 1 is designed to deliver a regulated output voltage VREG for powering an associated device, which is not shown. This regulated output voltage VREG is derived from a high level input voltage VHV of the order of several tens of volts, typically able to vary between 15 and 30 volts.
A voltage regulating circuit of this type is used in particular in smoke detection devices, as disclosed for example in European Patent document No. A1-0 759 602 for deriving a low level regulated voltage (for example 5 volts) necessary, amongst other things, for powering a microprocessor of the smoke detection device. In the scope of such an application, the line voltage powering the smoke detection devices is for example of the order of 15 to 30 volts.
Regulator circuit 1 of FIG. 1 typically includes a differential amplifier 4 one input of which is connected to the output of a voltage divider circuit 5, formed in this example of two resistors 51, 52 connected in series, the other input of differential amplifier 4 being connected to a reference cell 6 delivering a reference voltage VREF. This reference cell 6 is typically a cell delivering a temperature stable reference bandgap voltage. The output of differential amplifier 4 is directly connected to the gate of the JFET transistor forming regulator device 2.
The arrangement illustrated in FIG. 1 thus assures that the voltage present at the output node of voltage divider circuit 5, namely the connection node between resistors 51 and 52, is substantially equal to reference voltage VREF, the values R1, R2 of resistors 51 and 52 being chosen such that the regulated output voltage VREF of regulator circuit 1 has a determined value, for example of the order of 5 volts. This regulated voltage VREF powers in particular, differential amplifier 4 and reference cell 6 of regulator 1 as illustrated in FIG. 1.
One drawback of the regulator circuit of FIG. 1 lies in particular in the choice of external regulator device 2 and the costs of the regulator device. In the example of FIG. 1, it will be understood that the JFET transistor has to be chosen to resist relatively high drain-source voltages (in the example of the order of max. 25 volts), this drain-source voltage being in particular a function of the high input voltage VHV and regulated voltage VREF which one wishes to deliver at the output of the regulator. It will be noted that the cost of this JFET transistor increases with the maximum drain-source voltage to which the regulator element can be subjected. It is thus desirable, in particular with a view to reducing costs, to propose an alternative solution to the solution shown in FIG. 1.
Another drawback of the solution shown in FIG. 1 lies in the fact that the gate of the JFET transistor forming external regulator device 2 is directly controlled by the output of differential amplifier 4. The gate voltage of the JFET transistor is thus limited by the output voltage of differential amplifier 4, which is itself dependent on the technology used.
A serious drawback of the solution of FIG. 1 thus lies in the fact that its application is limited by the high input voltage capable of being applied to the regulator input and by the regulated output voltage which one wishes to deliver. Thus, if the high input voltage were increased and/or if the regulated output voltage were reduced, for example to 3 volts, the limits imposed by technology would make the use of the regulator circuit of FIG. 1 too expensive or even impossible, in particular when one wishes to manufacture this regulator in submicron technology.
The object of the present invention is thus to propose a solution allowing the aforementioned drawbacks to be overcome, and in particular to propose a solution allowing the use of a less expensive external regulator device and a solution able to be used with higher input voltages.
Another object of the present invention is to propose a solution able to be made and manufactured in a CMOS submicron technology, in particular in a 0.5 xcexcm CMOS technology.
Generally, according to the present invention, the external regulator device is advantageously controlled via a specific high-voltage MOSFET transistor capable of seeing at its terminals a drain-source voltage of the order of several tens of volts. Consequently, the stress imposed on the regulator device and on the differential amplifier is lower, this involving in particular lower costs as regards the external regulator device.
Although the present invention requires the use of additional elements, the additional costs caused by the addition of these elements are nonetheless less than the saving that can be hoped for on the costs linked to the external regulator device. Further, the high-voltage MOSFET transistors used within the scope of the present invention are perfectly compatible with standard CMOS technology and require little or no masks and/or additional implantation in order to be manufactured.
According to a preferred embodiment of the present invention, the regulator circuit is arranged to deliver a first regulated output voltage, or intermediate voltage, and a second regulated output voltage for powering certain components of the regulator circuit, such as the differential amplifier and the regulator reference cell, and for powering the electronic circuits of any associated device, such as for example the microprocessor responsible for the operations of a smoke detection device. According to this preferred embodiment, the intermediate regulated voltage is for example used, within the scope of application to a smoke detection device, to supply the current necessary for generating the infrared pulse via the infrared diode typically fitted to such detection devices.
Within the scope of application in a smoke detector and unlike the regulator circuit of FIG. 1, it will be noted that this preferred embodiment of the present invention enables the infrared diode to be moved from the input to the output of the regulator circuit where the intermediate regulated voltage is delivered. The voltage necessary to generate an infrared voltage pulse in a smoke detection device is typically of the order of tens of volts, i.e. well higher than the voltage levels used to power the electronic circuits of the device. According to this embodiment of the invention, this regulated intermediate voltage is of a lower level than the input voltage of the regulator circuit, thus allowing a reduction in losses when the infrared pulse is generated, and nonetheless higher than the supply voltage of the electronic circuits in order to assure an adequate supply voltage for generating the infrared pulse.
According to another embodiment of the present invention, the regulator circuit is arranged such that the differential amplifier controlling the external regulation device has a hysteresis, assuring in particular increased stability in the operation of the regulator.